1. Technical Field
The present invention relates to the field of power transmission, and more particularly, to a drive shaft system.
2. Discussion of Related Art
FIGS. 1A-1D illustrate a prior art drive shaft system 99 transmitting torque and rotation from a motor 60 through a coupling 50 to a rotor 70, e.g. of a compressor. Coupling 50 comprises two spring systems 51A, 51B (FIG. 1B) that provide a flexible connection between the shaft of motor 60 and shaft 80.
Drive shaft system 99 comprises a shaft 80 supported by at least two supports 65, 75 in a shaft housing 90. Supports 65, 75 comprise bearings 95, 98 (respectively) that position shaft 80 within shaft housing 90.
In the illustrated example (FIGS. 1A-1D), rotor side support 75 has bearing 98 that is mounted in shaft housing 90, and motor side support 65 has bearing 95 that is preloaded by springs 97A. Preloading of bearing 95 prevents its skidding. FIG. 2A illustrates a prior art configuration, in which rotor side bearing 98 is preloaded by springs 97B. At least one of supports 65, 75 enables some axial movement (for example into gap 92 in FIG. 1D) to accommodate thermal expansion of shaft 80.
In a vertical configuration of drive shaft system 99, supports 65, 75 are loaded in an axial direction by the weights of rotor 70 and shaft 80 and in a radial direction by unbalance forces 91 illustrated in FIG. 2B.
Two wear processes are possible in prior art drive shaft systems 99 that cause early failure at supports 65, 75 due to wear of the adjacent face of shaft housing 90 and outer rings 96 of bearings 95, 98 (FIG. 2B). The first wear process results from a turning of at least one of bearings 95, 98 upon the action of radial forces associated with the starting of motor 60 in combination with the large moment of inertia of rotor 70 and the flexibility of coupling 50. The second wear process results from radial movements of at least one of bearings 95, 98 during the high frequency rotation of rotor 70. Wear to bearings 95, 98 and to the adjacent face of shaft housing 90 occurs due to the radial movements in gap 92 between bearings 95, 98 and shaft housing 90 (gap 92 represents some freedom due to installation of bearings 95, 98 in shaft housing 90 without interference fit). Gap 92 further enables accommodation of shaft 80 expansion when bearing 98 is fixed (FIG. 2C). A similar gap may occur between the inner ring of bearings 95, 98 and shaft 80.
Debris 93 that accumulates as result of the wear processes increases the friction between supports 65, 75 and shaft housing 90 and prevents axial movement. In this situation, the system is susceptible to damage resulting from increased axial forces acting upon supports 65, 75, such as forces due to thermal expansion of shaft 80, damage that shortens the operation time of drive shaft system 99 or even causes complete failure and damage to rotor 70 and/or motor 60.
Prior art comprises elements that mild wear, such as cooling drive shaft system 99, and lubricating or coating the contact areas between bearings 95, 98 and shaft housing 90, however these elements do not solve the fundamental problem.
WIPO Publication number WO 03/086836 relates to a worm gear for a steering wheel of a motor vehicle, whereby the automatic interlock is independent from the sense of direction of torque (M) acting upon a worm wheel of the worm gear. The publication teaches pushing the worm gear upon the worm wheel.
WIPO Publication number WO 2009/047973 discloses the prevention of damage of smearing over a wide use conditions including high speed rotation and light load, and facilitating assembling of a shaft supporting device. In a shaft supporting device having a cylindrical roller bearing built between a rotating shaft and a housing, recesses are formed along the axial direction on the inside diameter surface of the housing and the outside diameter surface of the outer ring of the cylindrical roller bearing to face each other under a state where the cylindrical roller bearing is built in, and a preload regulation component is inserted between the facing recesses. Radial cross-section at the inserting portion of the preload regulation component has such a region as the radial dimension increases depending on the rotation angle about the axis in the axial direction. When the preload regulation component is rotated about the axis, the outer ring is pressed to the inside diameter while being interposed between the facing recesses, thus increasing the radial clearance of the cylindrical roller bearing to the negative side and the preload regulation component is locked under the state where the radial clearance is increased. U.S. Pat. No. 3,485,540 teaches a self-aligning bearing support for the journal of a high speed rotatable shaft that is resiliently supported by annular steel spring means having a comparatively low spring rate radially and portions spaced circumferentially for the unrestricted passage of lubricating fluid therebetween. The spring is compressed radially between the bearing support and an outer housing, which are closely spaced radially at a plurality of circumferentially spaced locations to effect an annularly arranged movement limiting clearance in communication with and interrupted by a plurality of circumferentially spaced regions of large radial clearance which also communicate with the spacing between the springs and with a drain to render oil film squeeze damping nominal at the movement limiting clearance. The housing and bearing are interlocked against relative axial and rotational movement by a portion of the lubricating oil duct system.